The main weight savings I made were in my pack, shelter and sleeping bag choices.
I made my own pack, which turned out at around 450 grams, a little smaller than my golite.
I made my own insulated hammock, with a pocket of down under it, which weighs a bit over half a kg. I'm pretty sure there's a pic of it in my gallery.
I also sewed a silnylon tarp, which weighs less than 250 grams
I use a JRB quilt instead of a sleeping bag. It weighs 425 grams and has kept me warm down to around freezing. It also has a head hole so it can be used as a warm poncho.
I don't always use this setup, sometimes I take another homemade hammock with a much heavier underquilt.
1.3kg for a hammock (I'm assuming that includes a tarp) does sound quite heavy. There are much lighter options out there if you want to go the hammock route.
check out
www.imrisk.com and
www.hammockforums.net
Congrats on cutting off 4kg, that's quite an achievement in itself.
If you or someone you know can sew, you'll find that's generally the lightest and cheapest way.
You're absolutely right about how the weight of small items add up. Even stuffsacks can add on a kg if you've got lots of them and they're heavy duty.